Increased concentrations of CO2 in the atmosphere will cause not only global warming but also raised partial pressure of CO2 and lowered pH in the ocean. These environment alterations may affect fish and other marine organisms. On the other hand, feasibility studies recently suggest that disposal of anthro-pogenic CO2 in the deep ocean could help reduce atmospheric CO2 concentrations. However, implementation of this strategy could have a significant environmental impact on marine life. These circumstances provide a background for the urgent need of further studies concerning the effect of CO2 on fish. In this paper we sum-marize the literature reporting on CO2 effects on fish and discuss the required research work for the future. The present knowledge from the literature is summarized and categorized into oxygen consumption rate, respiration activity, oxygen carrying capacity by red blood cells, blood gas, blood circulation, CO2 receptor, acid-base balance, endocrine, growth, toxicity and anesthesia. Most of the experimental fish used in the literature are freshwater species (carp and rainbow trout have largely been used). There were only few examined marine species (three bottom dwelling species of elasmobranch and teleost, respectively). Since experiments have only been carried out on adult fish, experiments on reproduction and the early life stage should be performed to clarify effects over the life cycle and to predict long term hypercap-nic effects. Physiological studies have mostly been concerned with the acid-base balance and we need further information on maturation and endocrine to evaluate long term hypercapnic effects on fish populations. Changes in swimming behavior and its mechanism must also be examined. Although the early phase of future study on CO2 effects on fish has to start using shallow-water species, deep-sea species should be considered in concern with the disposal of CO2 in the deep ocean. Furthermore, extrapolating data from one well researched species to evaluate implications on the ecosystem as a whole would be hazardous. In order to validate an appropriate resolution to the global warming problem, a multi-disciplinary approach to the effects of CO2 disposal utilizing spe-cialists from fields such as marine biology, fisheries and physical oceanography is clearly necessary.
The population size of the endangered bagrid, Pseudobagrus ichikawai, in the Kawaura River and its tributary, the Tsuzuya River (Nagara River system), was estimated by a combination of night-visual-census and mark-releaserecapture methods in 1996. The fish were distributed in patches in reaches of 6 km (Kawaura R.) and 2 km (Tsuzuya R.) out of 11km surveyed. Visual counts in all 235 pools in the surveyed area and mark-release-recapture experiments in five selected pools indicated that a correction factor of ca . 4.3 times was necessary for the former, a total of 1460±100 SE fish being present in pools . The total population including that in riffles was estimated as being less than twice that in the pools, with 40-50% of the total population constituting the reproductive group.The effective population size was likely to be less than this proportion, owing to a sex ratio bias towards females. Larger pools tended to be occupied by greater numbers of fish, both the number and density of fish in a pool being positively correlated with the number of fish in neighboring pools . These results suggested that movement between the pools is important for the persistence of the P. ichikawaipopulation, which is presently somewhat fragmented by many weirs on the river.
The growth and migration of the roughskin sculpin, Trachidermus fasciatus, were investigated using a mark-recapture method. Samples were obtained by casting net, hand net and trap at sites 0-7 km upstream from the estuary of the Kashima River, in 1993-1996. A total of 1, 029 individuals were marked, 75 being recaptured 105 times in total. Seasonal changes in the total lengths of captured and recaptured individuals indicated an annual growth of ca. 130-190 mm TL, with a period of growth stagnation in summer. Because only one population mode was apparent, the sculpin is thought to have a single-year life span. Individuals showed primarily upstream migration between May to July, eleven recaptured individuals having moved upstream during this period. From August to October, almost all recaptured individuals were taken at the same sites, as before, 6-7 km from the river mouth, the species apparently not the migrating long distances at this time. Subsequently, all sculpins disappeared from the 6-7 km sites by December, sixteen individuals recaptured downstream.
A stingray Himantura fai, collected from Iriomote Island (24°23'58'N, 123°47'05'E), the Ryukyu Islands, is described here as the first record from Japan. Comparisons with two congeneric species (H. gerrardi and H. uarnak) found in Japan reveal that this species is characterized in having a blunt snout tip, a dark long tail (length slightly over twice disc length when intact), higher count of intestinal turns (more than 28), and plainly dark brown coloration on dorsal part of disc. Its occurrence in Iriomote Island, the Ryukyu Islands, is the northernmost record of this species.
An engraulid fish, Stolephorus commersonnii Lacepede, collected at the lower reaches of the Miyara River (24°21'5', 124°12'45'E), Ishigaki I., Okinawa Prefecture constitutes the first record from Japan. One specimen (72 .5mm in standard length) of S. commersonnii is herein described with new Japanese name “Yaeyama-ainokoiwashi.” This specimen is the northernmost record of the species.
A holocentrid fish, Sargocentron praslin (Lacepede, 1802), collected within a depth of 15-50 m off around Meitsu, Nango-cho, Miyazaki Prefecture (two specimens) and Okinawa I., Okinawa Prefecture (three specimens), Japan, constitutes the third record from Japan. Five specimens of S. praslin (143-189 mm in standard length) are herein described with a new Japanese name, Kuroobi-ebisu, and the two specimens from Miyazaki represent the northernmost record of the species.
Three specimens (128-144.5 mm in standard length) of a polynemid fish, Polydactylus sextarius (Bloch & Schneider), collected by a large set net off the eastern side of Ooshima Island, Meitsu, Nango, Miyazaki, Japan, represent the first reliable record from Japan and the northernmost record of the species. Polydactylus sextarius is characterized as follows: six pectoral filaments, almost all pectoral fin rays branched, pectoral fin longer than pelvic fin, vomer without teeth and a large black spot anteriorly on the lateral line.